After all, why raise money to buy stock from insiders if they could sell it in a few months on the public markets?

One possible answer is that the company didn't yet have the financials to support its $5 billion private valuation.

Today's report implies that was the case. One of Roof's sources states that the company's “private-market valuation could not be substantiated by their revenues as a public company." Apparently the company is having trouble with its "revenue run rate," a key metric when looking at startups considering an exit.